This invention relates to X-ray diffraction systems. X-ray diffraction is a non-destructive technique for the qualitative and quantitative analysis of crystalline material samples, which are generally provided in the form of crystals or powders. In accordance with this technique, an X-ray beam is generated by an X-ray tube with a stationary anode, by a conventional rotating anode X-ray source or by a synchrotron source and directed toward the material sample under investigation. When the X-rays strike the sample, they are diffracted according to the atomic structure of the sample.
A typical laboratory system 100 for performing single crystal diffraction experiments normally consists of five components as shown in FIG. 1. The components include an X-ray source 102 that produces a primary X-ray beam 104 with the required radiation energy, focal spot size and intensity. X-ray optics 106 are provided to condition the primary X-ray beam 104 to a conditioned, or incident, beam 108 with the required wavelength, beam focus size, beam profile and divergence. A goniometer 110 is used to establish and manipulate geometric relationships between the incident X-ray beam 108, the crystal sample 112 and the X-ray detector 114. The incident X-ray beam 108 strikes the crystal sample 112 and produces scattered X-rays 116 which are recorded in the detector 114. A sample alignment and monitor assembly comprises a sample illuminator 118, typically a laser, that illuminates the sample 112 and a sample monitor 120, typically a video camera, which generates a video image of the sample to assist users in positioning the sample in the instrument center and monitoring the sample state and position.
The goniometer 110 allows the crystal sample 112 to be rotated around several axes. Precise crystallography requires that the sample crystal 112 be aligned to the center of the goniometer 110 and maintained in that center when rotated around the goniometer rotational axes during data collection. The 112 goniometer typically has a magnetizable mounting base with an extension on which a sample holder can be mounted.
One type of magnetic-style sample holder 200 that is commonly used with conventional goniometers is shown in FIG. 2. This sample holder consists of a Spine cap 202 with a collar 204 that fits over the goniometer mounting base extension (not shown in FIG. 2) and is magnetically held on the goniometer. A pin 210 with a central axis extends from the Spine cap 202. The collar 204 has a precise inside diameter 206 that mates with the outer surface of the goniometer mounting base extension to radially position the sample holder with respect to the central axis. A mounting face 208 seats against a corresponding face on the goniometer mounting base to axially position the cap 202. A conventional Spine sample holder is described in more detail in “Automation of Sample Mounting for Macromolecular Crystallography”, Cipriani et al., Acta Crystallographica, D62, pp. 1251-1259 (2006) which is hereby incorporated by reference in its entirety.
A crystal mounting arrangement 212 is affixed to the free end of the pin 210. The crystal mounting arrangement has a small sample well (not shown in FIG. 2) in which the crystal is placed for measurement. The crystal mounting arrangement 212 may, for example, be a Micromount™ crystal mount developed and sold by MiTeGen LLC, P.O. Box 3867, Ithaca, N.Y. 14852.
Traditionally, once a sample in placed in such a sample holder and the sample holder has been mounted on the goniometer mounting base, the sample is not expected to be aligned in the X-ray beam path. Consequently, the goniometer mounting base must be adjusted to position the sample in the center the X-ray beam. Traditional X-ray diffraction instrumentation has required either manual adjustment of a crystal sample position in the beam path, or more recently, automated positioning based on the use of an imaging system, such as illuminator 118 and imaging system 120, microscope, control software, and at least three linear actuators. These arrangements are complicated and expensive.